Chicago's mayor opened the city's arms wide Thursday to people who want to visit Grant Park for Barack Obama's Election Night rally—or just be near it. And as he did, the festivities promised a shortened work day for some employees in the Loop.

The Building Owners and Managers Association in Chicago sent a letter to building managers in the Loop suggesting they send tenants home by 3 p.m. Tuesday, said Jennifer Martinez, a spokeswoman for the city's Office of Emergency Management and Communication.

Classes after 3 p.m. at Columbia College were canceled, and college buildings will close at 6 p.m., according to an e-mail from Columbia's provost, Steven Kapelke.

"We're not closing," said Blackstone Hotel general manager Shakir Hussain, whose building at Balbo and Michigan Avenues is steps from the rally site. No hotels will, he added. "If anything, hotels will be staffing up!"

The suggestion is voluntary, Martinez said.

A permit request for the rally says more than 70,000 people will cram into the south end of Grant Park on Election Night.

And on Thursday, Mayor Richard Daley stoked the celebratory vibe, welcoming people downtown even if they don't have tickets and will have to gather outside the secure area.

Daley has estimated that the throng could reach 1 million. But he said Thursday he had no intention of discouraging attendance.

"You think I'm nuts? You think I'm not going to invite people down? This is a celebration," Daley said. "No way I'm going to tell people they should not come down and celebrate."

For the hundreds of thousands of Barack Obama supporters expected to assemble Tuesday in and around Grant Park, the event promises one of two scenarios: a raucous victory party, or the world's largest gathering of the disconsolate.

The Obama campaign and the City of Chicago is planning a huge Election Day rally in Grant Park. Details are sketchy, and apparently planners are still struggling with the logistics. Well, we have experience attending this sort of event downtown ( Lollapalooza, Independence Day fireworks,...